I would make an ad hominem attack, yes. I don't believe ad hominem is fallacious in this sense.
Orson Scott Card has expressed such a lack of humanity elswhere that I do not understand why I would spend my time deciding whether his other arguments have any merit. He has disqualified himself from my consideration.
I don't think that qualifies for an ad hominem at all. It's only ad hominem if the factor you're dismissing the author due to happens to be irrelevant to his current argument. That's not the case, I agree.
Having said that, I just want to make it clear that I don't know enough about him to agree with your position on him. I know he's anti-gay, and I've read the Ender books. That's about it.
Try reading "A Memory of Earth". It was the thirds and last Card book I read, after I read Enders Game and Enders Shadow, and disliked both, I was told that maybe I should just read a non-Ender book since I clearly just had something against the Ender universe. I saw "A Memory of Earth" at a yardsale for a dollar so I bought it without knowing anything about it besides that it was Card, and not Ender-universe.
Actually, don't try reading it. It is literally the worse book I've ever read. Confused and idiotic plot, cliched one dimensional characters, a serious sense of confused genre....
A few years later, I looked the book up on wikipedia and learned that it is his sci-fi version of The Book of Mormon.... yeah, the guy is a total hack.
Orson Scott Card has expressed such a lack of humanity elswhere that I do not understand why I would spend my time deciding whether his other arguments have any merit. He has disqualified himself from my consideration.